Revert "Add compressed backend textures to Metal"

This reverts commit b19c78ebad8485475a14f8bfcc006099a12fdc08.

Reason for revert: iOS failures

Original change's description:
> Add compressed backend textures to Metal
> 
> Bug: skia:9680
> Change-Id: I7a3759d60549fd5f9051f57df0f4918c307ea3c8
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/265402
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> Commit-Queue: Robert Phillips <robertphillips@google.com>

TBR=egdaniel@google.com,jvanverth@google.com,robertphillips@google.com

Change-Id: If0d3ddf061b693084e15438fe3c0ddd58a6fec88
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:9680
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/265759
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
3 files changed